Fluorescent lamp idling circuit

ABSTRACT

A circuit is described for operating a fluorescent lamp at a low power consumption idling level. The circuit provides a capacitive impedance in series between the fluorescent lamp and an AC supply. The capacitive impedance is selected to reduce the current flow through the lamp to a low idling level, yet full illumination may be quickly and reliably restored by effectively removing the capacitive impedance.

O United States Patent 1151 3,679,932 Murphy July 25, 1972 54] FLUORESCENT LAMP IDLING 3,130,347 4/1964 Harpley 315/98 CIRCUIT 3,201,645 8/1965 Strecker ..315/105 3,264,518 8/1966 Stauverman ..315/98 X [72] Invent James stamfmd' Conn" 3,463,964 8/1969 Privett et al ..315/97 x [73] Assignee: Pitney-Bowes, Inc., Stamford, Conn.

Primary Examiner-John S. Heyman [22] 1971 AtwrneyWilliam 1). Soltow, 11.. Albert w. Scribner, Martin [21 Appl. No.: 107,795 D. Wittstein and Louis A. Tirelli 52 us. or ..3l5/106, 315/240 [57] ABSTRACT 3 39/04 A circuit is described for operating a fluorescent lamp at a low [58] Flew of Search" "315/239, power consumption idling level. The circuit provides a capuci- 315/138 240 tive impedance in series-between the fluorescent lamp and an AC supply. The capacitive impedance is selected to reduce [56] References Cned the current flow through the lamp to a low idling level. yet full UNITED STATES PATENTS illumination may be quickly and reliably restored by effectively removing the capacitive impedance. 2,492,575 12/1949 Jacobsen.... ..315/l06 X 3,086,140 4/1963 Banios ..3l5/278 X 4 Claims, 2 Drawing Figures CON TROL CIR CUIT rLTl" I l -23 LlLJ \T /ZO E is $26 34 A.C. 44 4 6 j mmrimmzsm 3.679.932

- SHEUIUFZ' I FIG. I

IXI'EXTOR. JAMES D. MURPHY ATTORNEY CONTROL CIRCUIT Lil! FIG 2 v Q Q ATTORNEY FLUORESCENT LAMP IDLING CIRCUIT FIELD OF THE INVENTION This invention relates to an idler circuit for an electric lamp, and more specifically to a circuit which maintains a fluorescent lamp in a low power consuming standby state.

BACKGROUND Fluorescent lamps commonly comprise atransparent tube with thermionic electrodes positioned at the tube ends. An ionizable gas at low pressure is placed in the tube for gas discharge purposes. The gas discharge stimulates phosphors coated on the interior of the tube, and causes them to radiate energy.

The frequency of the output radiation from a fluorescent lamp can be chosen by selecting the type of phosphors employed. For example, ultraviolet emitting fluorescent lamps are commercially available, and may be used to illuminate luminescent coded credit cards. Luminescent markings on the credit cards may be formed of a normally invisible ink which, under ultraviolet stimulation, radiates at visible wavelengths. With such luminescent code markings on credit cards, owner and credit verification may be made in a manner known in the art. Typically, automatic credit card verifiers containing UV lamps are stationed at locations where articles or services to be charged are sold. It is desirable that such credit card verifiers operate reliably and rapidly to assure customer service.

Fluorescent lamps, however, are characterized by a delayed and flickering start-up which slows and interferes with the credit card verification process. Numerous electrical circuits have been proposed to accelerate the start-up time and reduce the flickering of fluorescent light sources, but none entirely avoids start-up problems.

THE INVENTION In a circuit for operating a fluorescent lamp in accordance with the invention, a capacitive reactance of predetermined magnitude is interposed in series between the fluorescent lamp and its AC power supply. The capacitive reactance is selected to swamp the inductive reactance of a commonly used inductive ballast, and to present a capacitive reactive load to the AC supply. The capacitive reactance is further selected to reduce the current flow through the fluorescent lamp to a low power consuming but discharge sustaining level. The fluorescent lamp may be instantly and reliably brought to a bright intensity level, however, for purposes such as ultraviolet credit card illumination, by effectively removing the capacitive reactance and applying full AC power.

An advantageous feature of an idler circuit in accordance with the invention resides in the low standby power consumption, while an electrical discharge is maintained in the fluorescent lamp so that full power illumination can be instantly restored.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a partially broken perspective view of a credit card verifier employing an idling circuit in accordance with the invention.

And FIG. 2 is a schematic electrical circuit diagram of a preferred embodiment of the idling circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG, 1, a credit card verifier is provided with a credit card receiving movable tray 12. The credit card 14 is provided with the usual visible identifying legends and normally invisible luminescent code markings 16. The luminescent code markings are formed of a material or materials which upon illumination by ultraviolet light respond by radiating light at visible wavelengths. These luminescent marks 16 provide uniquely coded information, for instance, to verify the authenticity and standing of the credit card 14.

A conventional fluorescent ultraviolet lamp 18 is emplaced over the area occupied by the credit card supporting tray 12 when it is fully inserted. A normally open, momentary closed type of push button switch 20 is disposed on the exterior of the credit card verifier 10 for starting the lamp 18. Starting switch 20 is connected in series with the lamp 18 and the AC power supply to cause an initial full energization of the lamp when the switch 20 is closed. After the starting switch 20 is opened, however, the lamp 18 is dimmed to a low power consuming idling level. Another push button switch 21 is mounted on the verifier unit 10 and used to initiate a credit card reading cycle of a control circuit 22, during which a relay 23 is operated, the lamp 18 is temporarily at full brilliance, and the tray 12 is drawn into the verifier 10 by suitable mechanisms (not shown) to move the card I4 into position to be illuminated by the lamp 18.

FIG. 2 illustrates the electrical circuitry employed to start and operate the ultraviolet fluorescent lamp 18 at both standby and full illumination levels. The AC line power is delivered through double pole single throw switch 24 which turns on the entire verifier unit 10, including a control circuit 22. The power flows along leads 26 and 28 to an idling circuit 30 and a ballast inductor 32. The fluorescent lamp 18 includes a pair of spaced-apart electrodes 34-36 which are connected in series with the idling circuit 32 and ballast inductor 32. A conventional fluorescent lamp starter component 38 is connected across the electrodes 34-36, and is formed of a normally open heat responsive bimetallic switch 40 located in a gas-filled housing 42. Idling circuit 30 includes the normally open starting switch 20 and a pair of normally open contacts operated by a relay 23, both in parallel with a capacitive network formed of a capacitor 44 in series with a small transient suppressing resistor 46.

At an initial start-up time, i.e. when on-off switch 24 is first closed, lamp starting switch 20 is also closed momentarily, so that the full AC supply power is applied through electrodes 34-36 and starter 38. Since thermal switch 40 is normally open, a gas discharge occurs within the starter 38, producing a local heating effect which eventually causes thermal switch 40 to close. The closing of that switch has two effects. First, the impedance of starter 38 decreases, causing a larger current to flow through electrodes 34-36. These electrodes then act as filaments, and are heated to thermionic temperature. Second, the thermal switch shorts out the gas discharge in the starter 38, allowing thermal switch 40 to cool and therefore reopen. This reopening of switch 40 occurs after the electrodes 34-36 have reached thermionic temperature, and suddenly interrupts the current flow through ballast inductor 32, causing a large voltage to be developed across the inductor. This large voltage is applied across electrodes 34-36, and is sufficient to break down the gas in the lamp I8, causing a gas discharge between the electrodes which illuminates the lamp brightly. At this point, the switch 20 has accomplished its lamp starting function, and may be released.

As long as the discharge in the lamp I8 is sustained, even at low idling illumination levels, the voltage between electrodes 34-36 is reduced to a level below the firing threshold of the starter 38. Therefore, thermal switch 40 remains open as long as a discharge condition prevails in lamp l8, and the starter 38 does not recycle. The gas discharge in lamp 18 also serves to keep the electrodes 34-36 heated to thermionic temperature for continued lamp operation.

When the lamp starting switch 20 is released and reopened, the capacitive network 44-46 is interposed between the AC line and fluorescent lamp 18. The capacitor 44 is of a size selected to present a large reactive impedance to the line current. Preferably the capacitive impedance is about ten times the inductive impedance of the inductor 32. Hence, the net effect of the capacitor 44 and inductor 32 is to present a capacitive load to the line supply, which advantageously reduces the dissipation of electrical power. The impedance of resistor 46 is very small, of the order of less than one tenth of the impedance of capacitor 44. Resistor 46 serves to suppress transients arising when capacitor 44 discharges on closing of starting switch 20 or relay contacts 23.

in a typical idling and start-up circuit for a 4 watt fluorescent lamp, capacitor 44 has a value of one microfarad, transient suppressing resistor 46 has a value of about 180 ohms, and the ballast inductor 32 a value of about 900 millihenries. The wire resistance of inductor 32 is about 60 ohms. With a line frequency of 60 cycles per second, the capacitive reactance is about 2,700 ohms and the inductive reactance about 340 ohms. When the fluorescent lamp 18 is fully illuminated, its voltage is approximately 28 volts, drawing a current of about 160 milliamperes. When the idler circuit is actuated by opening lamp starting switch 20, however, the current through fluorescent lamp 18 is reduced to about 50 milliamperes with a lamp voltage of about 35 volts. This reduced current flow is sufficient to maintain fluorescent lamp 18 in a glowing but dimmed condition.

But it may be instantly raised to full illumination by shunting the capacitive network 44-46, as for example by closing the normally open relay contacts 23. For automatic operation of the credit card verifier 10, the relay 23 responds to the control circuit 22, which may be a conventional device for carrying out a variety of functions automatically, including the transport of card tray 12 (FIG. 1) and the energization of relay 23, when its operating cycle is initiated by the closing of the read switch 21. After the operating cycle of the control circuit 22 terminates, the tray 12 is returned to its original position and the relay 23 is de-energized. The relay contacts then re-open, au omatically returning the lamp 18 to its dim discharge state.

The use of a capacitive reactance is found especially advantageous when one considers the power consumption of a resistor in place of capacitor 44. Such resistor having a value of about 2,700 ohms would consume about watts, which would not only waste power but also entail unnecessary bulk and heat dissipation within the credit card verifier 10. in contrast, in the idling circuit of this invention, the dissipation of resistor 46 is of the order of a half watt and the power consumption of capacitor 44 is negligible.

It will now be appreciated that this credit has the advantages of low power consumption during standby operation combined with rapid and reliable full fluorescent illumination during credit card reading operation.

Since the foregoing description and the drawings are merely illustrative, the scope of protection of the invention has been more broadly stated in the following claims; and these should be liberally interpreted so as to obtain the benefit of all equivalents to which the invention is fairly entitled.

I claim:

I. An apparatus for illuminating a gas discharge lamp powered by an AC source and wherein a starter circuit is employed including a series connected ballast inductor and a starter component, the improvements comprising:

an idling circuit having low loss and high capacitive reactance characteristics, said idling circuit including a capacitor connected in series between the lamp and the AC source and having a capacitive reactance substantially larger than the inductive reactance of the ballast inductor, the reactance of said capacitor being sufficient, in and of itself, to limit the current flow through the lamp to an idling level sufficient to sustain a reduced power discharge in said lamp, and

a switch connected across said capacitor, said switch selectively operated to shunt said capacitor and thereby increase the current through the lamp to the level required for normal illumination by the lamp.

2. The improvement defined in claim 1, wherein said idling circuit further includes a resistor connected in series with said capacitor across said switch, said resistor having a resistance value sufficient to reduce capacitive transient currents when said switch is operated, said resistance value being substantially less than the reactance of said capacitor.

3. The improvement defined in claim I, wherein the capacitive reactance of said capacitor exceeds the inductive reactance of the ballast inductor by a factor of approximately 4. The improvement defined in claim 1, wherein the capacitance of said capacitor is on the order of one microfarad. 

1. An apparatus for illuminating a gAs discharge lamp powered by an AC source and wherein a starter circuit is employed including a series connected ballast inductor and a starter component, the improvements comprising: an idling circuit having low loss and high capacitive reactance characteristics, said idling circuit including a capacitor connected in series between the lamp and the AC source and having a capacitive reactance substantially larger than the inductive reactance of the ballast inductor, the reactance of said capacitor being sufficient, in and of itself, to limit the current flow through the lamp to an idling level sufficient to sustain a reduced power discharge in said lamp, and a switch connected across said capacitor, said switch selectively operated to shunt said capacitor and thereby increase the current through the lamp to the level required for normal illumination by the lamp.
 2. The improvement defined in claim 1, wherein said idling circuit further includes a resistor connected in series with said capacitor across said switch, said resistor having a resistance value sufficient to reduce capacitive transient currents when said switch is operated, said resistance value being substantially less than the reactance of said capacitor.
 3. The improvement defined in claim 1, wherein the capacitive reactance of said capacitor exceeds the inductive reactance of the ballast inductor by a factor of approximately
 10. 4. The improvement defined in claim 1, wherein the capacitance of said capacitor is on the order of one microfarad. 